The object of the proposed studies is to test the hypothesis that the interaction between anti-CD1 reactive NK T cells and marginal zone B cells (IgM(hi) IgD(lo) CD21(hi) CD1(hi)) via CD1 is a critical step in the pathogenesis of lupus in two mouse models; hereditary lupus in NZB/NZW female mice and lupus induced in adoptive BALB/c hosts after the injection of anti-CD1 TCRalpha/beta transgenic T cells. In both models, this interaction is theorized to help activate the marginal zone B cells to secrete autoantibodies, such as anti-dsDNA antibodies, of the pathogenic IgG2a isotype. In vivo and in vitro experiments focus on purifying NK T cells, and on purifying the marginal zone B cells with appropriate mAbs by flow cytometry. We have recently shown that the marginal zone B cells from NZB/NZW mice are the only subset that spontaneously secretes IgM autoantibodies, and is also expressing the IgG2a constant region gene. The sorted NK T cells and non-NK T cells and a variety of B cells subsets from NZB/NZW and transgenic BALB/c mice will be incubated in vitro or transferred to adoptive hosts to determine whether pathogenic autoantibodies are produced resulting in clinical lupus (proteinuria, anti-dsDNA antibodies, increased mortality, etc.) in the adoptive hosts. We will perform immunohistopathological studies to search for the interactions between the critical T and B cells in the marginal zone of the spleen of mice with lupus. In addition, we will attempt to determine patterns of autoantibodies identified in the serum of BALB/c mice injected with anti-CD1 transgenic T cells and compare to NZB/NZW mice. The latter studies will use immunoprecipitation, Western blots, and protein chip arrays. We will assess the impact of anti-CD1 mAb treatment in mice that develop lupus by monitoring disease parameters as well as the spectrum of autoantibodies secreted. Finally, we will attempt to establish a line of NZB mice expressing the green fluorescence protein (GFP) transgene such that transgenic NZB/NZW mice can be used as donors of labeled B cell subsets. The latter cells will be transferred to non-transgenic NZB/NZW hosts to determine their contribution to IgG autoantibody secretion.